Add any plugin (#2801)

* Add any plugin

This adds the any plugin, a plain copy of coredns/any documented here
https://coredns.io/explugins/any/ as an external plugin.

Fixes: #2785

Signed-off-by: Miek Gieben <miek@miek.nl>

* Stickler bot nit

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/any/any.go

@@ -0,0 +1,32 @@
+package any
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/miekg/dns"
+)
+
+// Any is a plugin that returns a HINFO reply to ANY queries.
+type Any struct {
+	Next plugin.Handler
+}
+
+// ServeDNS implements the plugin.Handler interface.
+func (a Any) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	if r.Question[0].Qtype != dns.TypeANY {
+		return plugin.NextOrFailure(a.Name(), a.Next, ctx, w, r)
+	}
+
+	m := new(dns.Msg)
+	m.SetReply(r)
+	hdr := dns.RR_Header{Name: r.Question[0].Name, Ttl: 8482, Class: dns.ClassINET, Rrtype: dns.TypeHINFO}
+	m.Answer = []dns.RR{&dns.HINFO{Hdr: hdr, Cpu: "ANY obsoleted", Os: "See RFC 8482"}}
+
+	w.WriteMsg(m)
+	return 0, nil
+}
+
+// Name implements the Handler interface.
+func (a Any) Name() string { return "any" }